1. Field of the Invention
The present invention relates to motors wherein a rotation speed detection mechanism including a magnet and a magnetic sensor is employed for detecting the rotation speed of the motor.
2. Description of the Prior Art
Air conditioning apparatus are typically provided with a fan device for generating an air stream flowing through a heat exchanger and into a room to be cooled or heated. The fan device is rotated by a motor, the rotation speed of which is detected by a rotation speed detection mechanism. The rotation speed of the motor is varied in response to the temperature of the room.
One example of a rotation speed detection mechanism is shown in Japanese Utility Model Laid-open Publication No. 62181/1980 laid open to public inspection on Apr. 26, 1980. In this prior art, a rotation plate is fixed on a rotation axis of a motor. The outer surface of the rotation plate is magnetized with alternating N-poles and S-poles. A circuit substrate for the motor faces the rotation plate. A Hall-effect IC is fixed on the substrate such that the detection surface of the Hall-effect IC 5 is opposite to the outer surface of the rotation plate. The Hall-effect IC includes a Hall element for generating a rotation detection signal which has a frequency responding to the rotation speed of the motor.
In the construction described above, since the rotation detection mechanism including the rotation plate and the Hall-effect IC is provided outside of the motor, an overall assembly of the motor is large. However, it has been desired to reduce the thickness of air conditioning devices in recent years. Taking such desire into consideration, a compact motor including a rotation speed detection mechanism is desired in air conditioning apparatus.